The present invention relates to the field of seismic cable recovery. More particularly, the present invention provides a system for retrieving seismic cables and attached buoys from a body of water.
Marine seismic operations utilize floating buoys and attached cables to suspend streamers, air guns and other equipment. The buoys mark the geographic position and orientation of submerged seismic equipment and provide a surface point of attachment for retrieving such equipment. The submerged streamers typically comprise communication lines for transmitting signals, cable stress bearing elements, and hydrophones for detecting seismic source waves reflected from subsurface geologic formations. The hydrophones convert the acoustic waves to signals which can be processed to evaluate the geologic formation structure.
Submerged seismic components are removed from the water to repair defects and to move the components to another location. A work vessel provides a floating base for capturing the buoy and for removing the buoy, cable, and seismic components from the water. In conventional cable retrieval operations, deck hands manually snag a buoy with grappling guns, hooks, poles or lines. The buoy and attached cable are manually pulled over an extended beam or "cathead" onto the vessel deck, the buoy is detached from the cable, and the cable is engaged with a rotating drum or wheel for winching the cable onto the vessel deck. As the cable is retrieved, seismic components are detached from the cable for storage on the vessel deck.
Manual seismic cable retrieval operations are cumbersome, hazardous, and frequently cause injuries. The risk of injury is particularly acute in rough seas when the vessel heaves and pitches relative to the buoys and seismic cables.
Various retrieval systems have been proposed to recover buoys and cables from water. U.S. Pat. No. 3,993,011 to Garland (1976) disclosed a mechanism for retrieving and launching barge anchor buoys. A cradle was positioned underneath a buoy, the cradle was pivoted upwardly to lift the buoy from the water, and the buoy was moved to the stern deck of a service vessel.
In other systems, U.S. Pat. No. 4,552,086 to Boe et al. (1985) disclosed a boom having hoist wires engaged with hoisting drums on a longitudinal axle. The axle was attached to suspension drums having wires for supporting submerged air guns below the axle. Rotation of the suspension drums raised the air guns relative to the axle, and the hoist wires were reeled in to lift the axle relative to the boom. In another system, U.S. Pat. No. 4,798,156 to Langeland et al. (1989) disclosed a winch for retrieving a cable over a guide pulley. Side mounted derricks were manuevered with hydraulic cylinders to draw the cables toward the vessel, and rear mounted derricks were operable to move cables deployed from the vessel stern. Additionally, U.S. Pat. No. 4,798,158 to Langner (1989) disclosed a docking cone for engaging one end of a seismic float. The docking cone could be raised to elevate one end of the seismic float, and a "latching saddle" or cables secured the float to the vessel.
Although these systems provide various techniques for reeling in buoys, cables and attached components, none of these systems provide an efficient system for retrieving seismic cables and attached components. Accordingly, a need exists for an improved retrieval system that facilitates the safe capture and retrieval of seismic cables and attached components.